In recent years, wireless communication technologies have developed rapidly, and 3GPP (the 3rd generation partnership project) standardization has developed to Rel. 12 (Release 12), key technologies of which covering wide configuration of small cells, carrier aggregation, and 3D (three dimensional) multi-antenna technologies (MIMO, multiple-input multiple-output), etc. Even though it has made a breakthrough in many transmission technologies, considering rapid development of mobile traffics at present and in the future and variety of terminal forms and enormousness of terminal numbers, capacities of LTE (long-term evolution) systems based on licensed bands will still be insufficient at present and in the foreseeable future.
On the one hand, the licensed bands are obtained by the operators through bids at the auction from telecommunications markets, which are high in costs. Hence, all levels of participants in the communication industry will guarantee the full use of these licensed bands by making standard protocols. With the development of technologies in these years, a tradeoff between the cost and effect has been reached in the communication technologies based on licensed bands. And on the other hand, there exist large quantities of unlicensed bands out of the licensed bands delimited by the ITU (International Telecommunication Union), which may be arbitrarily used while satisfying conditions of policies. For example, at a band of 2.6 GHz, which will possibly be 5.0 GHz in the future, there exist a large amount of WiFi (wireless fidelity) applications at the band of 2.6 GHz currently, which may be deployed by operators, and may also be deployed by vendors in markets. Considering that the large amount of unlicensed bands are vacant, participants in the LTE industry start to consider how to introduce the LTE technology into these bands.
It is shown by studies that at these unlicensed bands, the use of the LTE technology will bring a larger system capacity than the use of the WiFi technology, this is because that an LTE system possesses more flexible physical layer transmission technology and MAC (media access control) layer physical resource allocation technology, as well as more advanced QoS (quality of service) administration, etc. Based on these conclusions, consideration of how to use the LTE technology at these unlicensed bands has been started in many studies. A key issue at present is that if the LTE technology is used, interference on the existing WiFi or other systems occupying these unlicensed bands must be strictly controlled.
The interference control technology adopts simple LBT (listen before talk) mechanism in the WiFi system, that is, an access terminal (a station, STD) monitors whether there exist other link data in a link before it prepares for transmitting data. If yes, it monitors again after waiting for a period of time. If no, it will transmit data after a period of time of delay. However, there is no strategy dealing with interference on other access points (APs, which have already occupied the channel) brought about by a wireless AP in transmitting data.
A function of selecting a channel by an AP is added into a protocol in a revised version of the WiFi standard IEEE802.11, that is, when it is detected that a channel is used by another AP, the AP selects another channel to monitor. If the LTE also adopts the similar LBT mechanism in the WiFi in using these unlicensed bands, it will appear that measurement of interference is inaccurate.
Generally speaking, when resources at unlicensed bands are used, a scenario of heterogeneous deployment where a macro cell and small cells coexist is employed, wherein, in the macro cell, a macro eNB is responsible for coverage of UEs, and in the small cells, low power eNBs are responsible for data offloading of UEs. Typical small cells include micro cells, pico cells, femto cells, and remote radio heads (RRHs). In comparison with the low power eNBs of the small cells, the transmission power of the eNB of the macro cell is relatively large.
Two examples are given below to explain the defect of the use of the general LBT mechanism in an LTE network. As shown in FIG. 1, terminal UE is within a coverage range of a WiFi AP, while it is also within a coverage range of a small cell in preparation for using an unlicensed band, and both the WiFi AP and the small cell are at sides of the UE. It is obvious that as the small cell is not within the coverage range of the WiFi, if the LBT mechanism is adopted, it is very possible that the small cell selects a channel identical to that selected by the WiFi AP. However, as the UE is within the coverage range of the WiFi AP, it will result in that the UE cannot correctly receive data from the small cell, since interference will be brought about by use of identical channels by the WiFi AP and the small cell. Likewise, as shown in FIG. 2, the small cell is located between the UE and the WiFi AP, and at this moment, the UE is out of the coverage range of the WiFi AP. If the LBT mechanism is adopted, the UE may use a channel identical to that used by the WiFi AP for transmitting and receiving data. However, as the small cell is very close to the WiFi AP, it will result in that the small cell cannot receive data from the UE correctly, and at the same time, interference will be brought about to the WiFi AP when the small cell transmits data in the channel.
It should be noted that the above description of the background is merely provided for clear and complete explanation of this disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of this disclosure.